Along with the recent development of information and communication technology, various wireless communication technologies are under development. Among them, WLAN is a technology that enables wireless access to the Internet through a portable terminal such as a Personal Digital Assistant (PDA), a laptop computer, a Portable Multimedia Player (PMP), etc. in a home, an office, or a specific service area by radio frequency technology.
To overcome the limitations of WLAN in communication speed, the recent technology standards have introduced a system that increases network speed and reliability and extends the coverage of a wireless network. For example, Institute of Electrical and Electronics Engineers (IEEE) 802.11n adopts Multiple Input Multiple Output (MIMO) using multiple antennas at both a transmitter and a receiver in order to support High Throughput (HT) with a data processing rate of up to 540 Mbps, minimize transmission errors, and optimize a data rate.
Machine-to-Machine (M2M) communication is under discussion as a future-generation communication technology. IEEE 802.11 WLAN is also developing a technology standard for M2M communication as IEEE 802.11ah. For M2M communication, a scenario in which a small amount of data is transmitted at a low rate intermittently in an environment with a large number of devices may be considered.
Communication is conducted through a medium shared among all devices in a WLAN system. If the number of devices is increased as in M2M communication, a channel access mechanism needs to be improved more efficiently in order to reduce unnecessary power consumption and interference.